Devices are known in the prior art which are insertable into the chamber of a firearm, and which emit a beam of light. In general, these devices are used to bore sight the firearm, or to simulate target shooting. For example, U.S. Pat. No. 4,481,561 to Lanning discloses a gun bore sighting flashlight insertable into the breach of the rifle, shotgun or pistol. The flashlight is activated upon breach closure, and aids the user in checking the sights of the firearm to assure that when the firearm is fired, the shot pattern will be directed at the same place that is visible in the sights of the gun.
U.S. Pat. No. 3,471,945 to Fleury discloses a light emitting shotgun cartridge. The shotgun cartridge consists of a cylindrical shell casing of a diameter suitable for insertion into the breach of a conventional shotgun. The cartridge employs a time delay circuit to simulate the actuatl projectile velocity, and therefore can be used to practice shooting at moving targets under field conditions.
Because the barrel of a firearm can become contaminated with rust, lead, powder residue, or other defects, it is necessary to periodically inspect the barrel. Devices such as those disclosed by Lanning and Fleury are not suitable to this task, however, since they emit a strong light down the length of the barrel that would temporarily blind an observer looking down the barrel.